The red imported fire ant, SOLENOPSIS INVICTA, was accidentally introduced into the United States from South America in the 1920's via Mobile, Ala. Since then its habitat has spread across all of the Southern United States as far west as presently near the Pecos River valley in Texas and to the Atlantic Ocean on the east. It ranges from the Gulf of Mexico as far north as Tennessee and North Carolina. This pest is very aggressive and has largely replaced native North American fire ants in the areas it infests.
SOLENOPSIS INVICTA can sting repeatedly and will attack anything that disturbs its nests or mounds or its food sources. Symptoms of a sting inflicted on humans include burning and itching. The venom which is injected can cause a white pustule to form in a day or two which can leave permanent scars. The stings are not usually life threatening but multiple stings can cause secondary infections and, in sensitive persons, can cause chest pains or nausea.
Attempts to chemically control SOLENOPSIS INVICTA in the 1960's, 70's and 80's used chemicals which also destroyed native ant species and may have actually aided the spread of these pests. Chemicals provide only temporary control of the ants and must be reapplied periodically for as long as control is desired. The application of chemical controls over long time periods can have other undesired side effects if the applications are cumulative. Because of these and other problems associated with chemical control, it would be highly desirable to control SOLENOPSIS INVICTA by use of a biological agent which would be essentially harmless to mammals and to other desirable insect species.
It has been known that effective control of some insect species, such as fleas, may be obtained by the use of nematodes. In particular some commercial nematode preparations are offered for this purpose such as BIOSAFE, made by the Solaris Group of San Ramon, Calif. and BIO FLEA HALT made by Farnum Pet Products of Phoeniz, Ariz. Nematodes of the families STEINERNEMATIDAE are symbiotically associated with bacteria of the genus XENORHABDUS. However, a study of the response of SOLENPOSIS INVICTA by Drees et al (Journal of Economic Entomology 85(2); 365-370; 1992) to nematode treatment in the field which included drenching SOLENPOSIS INVICTA mounds with solutions (of about 10.sup.6 nematodes per mound) of STEINERNEMA and HETEROHABDITIS NEMATODES showed that such drenching primarily caused relocation of the SOLENOPSIS INVICTA to satellite mounds in the vicinity. This same study showed, however, that under laboratory conditions SOLENOPSIS INVICTA larvae were moderately (78-100%) susceptible to infection by each nematode species tested in high dose ranges (10.sup.5 nematodes per sample dish) and by a lesser amount (38-88%) in lower dose ranges (10.sup.3 nematodes per sample dish). Also noted was that in the higher dose ranges more than 20% of the worker ant SOLENOPSIS INVICTA died, although these ants were shown not to be susceptible direct infection by the nematodes. Moreover, the use of the nematodes as a vector for infection by the bacteria limits the shelf of life of the control product to that of the nematode host, a matter of a few weeks.
It has been known that anitbiotics possessing antibacterial, antifungal, anti-inflammatory and antiulcerogenic properties can be derived from cultures of bacteria of the genus XENORHABDUS. For example, such compounds and their uses are disclosed in U.S. Pat. Nos. 4,837,222 and 4,672,130. However, experimentation done previously has been suggestive that the nematode host of the XENORHABDUS was necessary to introduce the bacteria into the system of a target animal as it was believed that XENORHABDUS did not survive well in soil or water and were not pathogenic for insects when ingested. See ENTOMOPATHOGENIC NEMATODES IN BIOLOGICAL CONTROL, CRC Press, Boca Raton, Fla.,1990, Chapter 4, pp. 75-89.